1. Field of the Invention
The invention relates to a C2/m-structured cathode material, and more particularly to a C2/m-structured cathode material for a lithium-ion battery. The invention also relates to a lithium-ion battery containing the C2/m-structured cathode material.
2. Description of the Related Art
A lithium-ion battery generally includes an anode containing LixC, a cathode containing metal oxide or phosphate, a polymeric separator for separating the anode from the cathode, and an organic electrolyte solution containing a lithium salt. Conventional cathode materials include a layered-type oxide of LixMO2 (M=Co or Ni), Spinel structured LixMn2O4, or Olivine structured LixFePOx. For the layered-type oxide of LixMO2, however, x is required to be equal to or larger than 0.5 in view of structural stability of the cathode material, and specific capacity of the layered-type oxide of LixMO2 is typically lower than 140 mAh/g.
WO 2008/137241 A2, which corresponds to US 2008/0280205, discloses a layer-structured cathode composition for a lithium-ion battery. The cathode composition has a formula of Li[LixMnaNibCOcM1dM2e]O2, wherein M1 and M2 are different metals and are not Mn, Ni, or Co; x+a+b+c+d+e=1; −0.5≦x≦0.2; 0≦a≦0.80; 0≦b≦0.75; 0≦c≦0.88; 0≦d+e≦0.30; and at least one of d and e is larger than 0. The cathode composition has a space group of R-3m, and is in a form of a single phase having a layered O3 crystal structure. The cathode composition has a stable interlayer structure and is not liable to collapse due to movement of lithium ions from and to the layer-structured cathode composition. Therefore, the structural stability and the specific capacity can be enhanced. However, the specific capacity of the layer-structured cathode composition is usually not greater than 180 mAh/g.